1. Field of the Invention
The present invention relates to a storage system and a data migration method therefor and, more specifically, to a data migration technology between logical volumes.
2. Description of the Related Art
With the recent increase of the data processing amount in a computer system, a storage device, i.e., storage subsystem, in charge of data storage has been increased in capacity. Accordingly, such technologies as SAN (Storage Area Network) and NAS (Network Attached Storage) have become widely used. With these technologies, the system management can be performed with flexibility and efficiency with a storage device connected to a plurality of host computers over a network.
In recent years, the demand has been growing for reduction of the operating cost of the storage device. For reduction of the operating cost as such, data life cycle management is a solution. With data life cycle management as such, data management is so performed that data is reallocated to any appropriate storage device in accordance with the storage date and time of data and the use frequency thereof, for example. For implementing such data life cycle management, data migration is known as a technology of migrating data on a volume in the storage device to another volume therein.
With such data migration, typically, the storage device firstly copies data on a volume being a migration source to a volume being a migration destination, and then deletes the data on the migration-source volume before changing an access destination from a host computer to the migration-destination volume. During such data migration, if a writing request comes from the host computer to the migration-source volume, the storage device stores data requested for writing in a cache memory as update data, and then reflects the update data to the migration-destination volume, thereby keeping the consistency among the volumes.
Patent Document 1 (JP-A-2007-279845) below describes the technology of reallocating a volume to another volume in accordance with migration essential conditions. To be specific, for reallocating a first volume in a first storage tier into a second storage tier, the storage system of Patent Document 1 operates as below. That is, if the second storage tier includes no second volume satisfying the migration essential conditions to serve as a migration destination for the first volume, the storage system temporarily allocates any of volumes in a third storage tier satisfying the migration essential conditions, i.e., a third volume, to the second storage tier so that the first volume is reallocated to the third volume.